1. Field of the Invention
This invention relates to a circuit unit comprising at least an insulating substrate on which a conductive coil is located, and an integrated circuit whose connection points are electrically connected with the coil ends. The invention relates further to a method for producing such a circuit unit.
2. Related Technology
Circuit units of the above type are known from the prior art, being designed for example as compact electronic modules which are inserted in chip cards for noncontacting data exchange with a terminal. For example U.S. Pat. No. 4,999,742 discloses a circuit unit in the form of an electronic module with an insulating substrate on which a ring-shaped wound coil is glued. The coil ends are guided into the receiving space arising through the ring-shaped coil, and electrically connected there with the connection points of an integrated circuit. The receiving space for the integrated circuit and coil ends is cast with a casting compound for protecting these sensitive components from mechanical loads.
The electronic module known from U.S. Pat. No. 4,999,742 has a compact structure but the coil must be wound in a separate method step and glued on the insulating substrate in a further method step.
However, the as yet unpublished German patent application P 44 16 697.4 discloses a circuit unit in the form of a chip card having printed on one card layer of the multilayer card body a coil from a conductive lacquer whose ends are electrically connected with the connection points of an integrated circuit.
The structure of the circuit unit known from patent application 44 16 697.4 has the advantage that the coil is printed directly on a card layer so that the method step of applying a separately manufactured coil to an insulating substrate is omitted. For some applications of the circuit unit, however, it is desirable for the coil to have a higher number of turns than can be realized with the structure explained above. Furthermore it may be desirable to provide the circuit unit with relief embossing. One must then make sure the printed turns of the coil, which are generally formed as a very thin layer, are not interrupted. Also, the production method for the circuit unit should be further optimized with regard to inexpensive mass production.
From U.S. Pat. No. 4,960,983 (Inoue) a circuit unit in the form of an IC card is known. The IC card comprises an electronic module with a coil structure being formed on the semiconductor substrate of the electronic module. A coil may be formed of two or more coil structures which are deposited on different metallic layers having insulation layers between the metallic layers whereat the metallic layers are interconnected by means of a central conductive member which extends between the distinct metallic layers.
However, the Inoue patent teaches forming the coil on the substrate of the IC chip. As the production of semiconductor devices is very expensive and the yield depends directly on the area of semiconductor covered by the IC chip, the teaching of Inoue has both the disadvantage of high cost and low yield as the area covered by the an IC comprising coil structure is enormous. The size of the IC chip has the further disadvantage of being susceptible to mechanical stress. The IC chip is embedded in the card body which is flexible therefore torsion or bend may destroy the IC card or the IC chip.
From JP 6 336096 a chip card is known which is produced from two insulating substrates. Each of the substrates has a coil pattern. After connecting the two substrates by an insulating adhesive the two coil patterns form one coil.
However, as it is stated expressly not to use a through hole for contacting the two coil patterns and as the coil patterns are formed on different substrates, chip cards having coil layers and insulating layers which are applied alternately to a substrate are discouraged.
From EP 0 547 563 B1 a printed circuit board antenna is known which has a plurality of different coil layers. However the European patent does not show the use of an IC chip. In particular this is a disadvantage because the two coil ends are on different sides of the circuit board. If an IC chip is to be mounted on one side of the circuit board an additional through hole is necessary to connect the IC to the second end of the coil. Additional connectors are also necessary to connect the different layers of the coil which is especially a disadvantage because an additional step is necessary to insert the connectors.
It is therefore the problem of the invention to further improve the abovementioned circuit unit and at the same time in particular to extend its range of applications. It is further the problem of the invention to propose a method for producing such a circuit unit.